This invention relates to the preparation of 2-chloro-4-toluenesulfonyl chloride from toluene in a chlorinated hydrocarbon medium.
Direct chlorination reactions of aromatic compounds are often nonselective in aromatic systems and give a random distribution of chlorinated derivatives. The inadequacies of direct chlorination as a method of producing aryl chlorides have brought about attempts to utilize the more selective substitution patterns of sulfonation reactions. However, known methods for effecting selective chlorination by means of the sulfonation of aromatic compounds have not been implemented commercially because the separate steps of selective sulfonation, nuclear chlorination at other sites, conversion to the sulfonyl chloride, and displacement of the sulfonyl chloride group by a chlorine have required different reaction mediums and conditions to effect each of the desired intermediates in high yield. Each process step, of course, adds considerable expense to the overall process and makes commercialization economically unattractive.
Consequently, direct chlorination, as recited in U.S. Pat. No. 4,045,502, is the conventional commercial process employed by the art to prepare 4-chlorotoluene from toluene, despite the concurrent production of a high proportion of other monochlorotoluene isomers.
The practice of this invention is useful to prepare a basic intermediate for a number of dyes, herbicides and other useful compounds. This invention is particularly useful in the preparation of 2,4-dichlorobenzotrifluoride, a precursor of commercial herbicides as illustrated in British Pat. No. 1,321,563.